1. Field of the Invention
The present invention relates to a control apparatus for a heater provided in a grip of a steering handle of a vehicle such as a motorcycle, a snowmobile, or a wet bike.
2. Related Background Art
Conventionally, there is an already known technology of providing a comfortable driving environment for a driver by providing a heater (an electric heater) in a grip (a part gripped by the driver) of a steering handle and controlling the amount of electricity supplied to the heater to warm the grip in a vehicle having an engine as a propulsive source such as a motorcycle, a snowmobile, and a wet bike (for example, refer to Japanese Laid-Open Patent Publication No. 2004-75047 (hereinafter, referred to as patent document 1)). The apparatus in the patent document 1 has a variable resistor in a circuit for controlling the amount of electricity supplied to the heater and adjusts the amount of electricity supplied to the heater by changing a resistance value of the variable resistor with a dial control for adjusting a temperature provided at the end of the grip to adjust a temperature of the heater.
Moreover, a battery used for supplying electric power to the heater supplies electric power to an electric system of the entire vehicle such as a starter motor or lamp, and thus the heater control of the grip is an appendant for the vehicle. Therefore, there is a need to give priority to traveling of the vehicle when supplying battery electric power. Therefore, there has been suggested a grip heater control apparatus for halting power supply from the battery to the heater before the battery voltage drops below a minimum voltage required to start the engine (drive the starter motor) (for example, refer to Japanese Laid-Open Patent Publication No. 2004-67076 (hereinafter, referred to as patent document 2)).
The heater control apparatus in the patent document 2 performs heating by controlling electricity supplied to the heater from the battery by the PWM control in response to a switch operation for temperature adjustment performed by a driver. Moreover, the control circuit is provided with a battery voltage detection and determination unit for detecting a battery voltage. Where the battery voltage has reached a predetermined voltage close to the minimum voltage required to drive the starter motor, the battery voltage detection and determination unit forcibly turns off the electricity to the heater and notifies the driver of the battery voltage drop.
On the other hand, the battery is charged by a power generator for generating electricity interlocking with the rotation of the engine. Thus, the amount of power generation of the generator becomes smaller in proportion as the number of engine revolutions decreases.
In the grip heater control apparatus disclosed in the patent document 1, however, if the driver operates the dial for temperature adjustment to increase the temperature of the heater at a low engine speed, the amount of electricity to the heater becomes excessive relative to the amount of power generation of the generator, which could lead to a situation where the battery voltage drops below a minimum voltage required to drive the starter motor. Meanwhile, in the grip heater control apparatus disclosed in the patent document 2, the battery voltage can be prevented from dropping below the minimum voltage required to drive the starter motor, but the heater is forcibly turned off more frequently by the operation of the switch for temperature adjustment to increase the amount of electricity to the heater at a low engine speed. This increases the occasions where the driver cannot warm the grip when he desires. Particularly when the battery supplies power to a lamp or other electric equipment other than the heater or when the battery voltage cannot go up enough due to the battery deterioration, the grip heater control apparatus has a disadvantage of increasing the cases where the driver substantially cannot operate the heater.